Even if GNOME doesn’t officially support desktop widgets, programs can always just place themselves on the desktop and act like a desktop widget would.
And there are certainly some desktop environment agnostic desktop utilities/widgets (which work on GNOME) out there.
First of all, only X11 clients can manipulate the window stacking order and ask to be placed at the bottom of the stack programmatically; this cannot be done with Wayland, where the user must be involved with any stacking operation.
Second of all, “widgets” on the desktop are not identified as a special case by GNOME, so they would just be windows. One thing that would immediately break is dynamic workspaces, as then no workspace would ever be closed if it contained “widgets”.
GNOME simply does not support desktop “widgets”. If we ever wanted to support them, they would likely be a separate, specialised workspace, and would have a special window type.
It has been some time but I have used nemo-desktop for desktop icons with no problem regarding workspaces. The only problem it had was that it did not autostart properly sometimes.
As far as I know, it is also an XWayland client and shows itself on the desktop on every workspace.
Edit: Tested it just now. Still works on 43 Wayland.